It is often hard to think up new projects that are within the scope of what we have just learned. The following are some useful instruments and controllers that you now have the skills to build. Each can be embellished to showcase your newly learned skills, and each one teaches you another skill. Some projects are harder than others. Points are awarded for how well the instrument works (engineering) and how good it looks (workmanship and design).
1. Build a finished useable instrument that will tell you how fast you are accelerating or decelerating as you move forward or backward in your car, and how many g-forces you experience as you go around a corner. Display the information in real time on the two lines of a 2-line-by-16-character LCD display. As an added bonus, you are asked to add an alarm that goes off if you exceed certain acceleration values and create the ability to record the maximum accelerations experienced during any one trip. (Would it be possible to integrate the g-force over time to tell how fast you were moving, and do you have the skills to do this? What are the problems involved and what kind of accuracy can you expect. Could some simple experiments allow you to determine if you are on the right track? What are these experiments?)
2. Build a rudimentary carpenter’s level with a digital display that tells you how far from horizontal the level is in units of 0.1 degrees. Display your results on a 1-line-by-16-character LCD display. Added bonus: add an LED that blinks as long as the instrument is kept level within 0.3 degrees to the horizon.
3. Build a rudimentary digital protractor that will allow you to place an object at any angle to the horizon within 0.5 degrees. (Hint: You must use both axes of the Memsic and switch between them at 45 degrees.) Display your results on a 1-line-by-16-character LCD display. Added bonus: provide a written discussion of the accuracy that can be obtained with the detector being used, and discuss what the limiting factors are. Discuss what fabrication problems you encountered during construction and what the software problems were. Where is the protractor most and least accurate? Provide a table of + and – error probability values for every 5 degrees.
4. Build an 18-inch diameter wall thermometer that uses one R/C servo to directly connect to and drive the indicator/needle of the thermometer. These servos have a range of about 180 degrees. Use 100 degrees of this range to indicate a temperature from −30 to +120 degrees. Use the LM34 as your temperature sensor.
5. Build a 12-inch diameter thermometer similar to the one in project 4 that uses a small and inexpensive 200-step-per-revolution stepper motor as the driver for the thermometer needle. Use an appropriate thermistor as your detector and calibrate it for this application. Since the position will be lost during a power failure, your software must provide the features needed to zero against a stop and thus start the servo from a known position every time. This is the technique used for most computer-controlled instruments in automobiles and in industry. (All this can be done with cardboard construction techniques.)
6. Build a small voltage monitor to monitor and display the conditions of your car battery terminals at all times. Design this so it can be mounted on your dash.
7. Build an accessory for your soldering iron that lets you control the temperature at the tip of the iron by turning the iron on and off. Display the tip temperature and provide an LED to indicate the “power on” at the iron. Use a tiny thermistor attached a ½ inch from the tip as your sensor. The temperature should be nearly constant across the copper tip.
8. Build a combination speedometer and odometer for use on a bicycle. The unit must detect wheel rotation at least four times per revolution. Allow the input of the wheel diameter in inches.
9. Build a detector and motor driver that will allow a solar collector to remain aimed at the sun all day to optimize the collection of solar energy. Power it using a stepper motor or a servo motor. Only one axis needs to be moved.
10. Build a ¼-second pendulum that is accurate to one cycle of the MCU clock. An iron bob on the end of a string will do. Provide the software to slow down or speed up the pendulum as necessary to stay in time with the signals provided by the microprocessor clock, the ¼-second time signal that you will have created for this project. (Hint: You will need a couple of coils to push and pull on the iron bob to keep the system in sync with the microprocessor signals.) This exercise should demonstrate that even fairly simple techniques can be used to create an accurate pendulum for a clock. Discuss how this technique could be used to improve the accuracy of an aging grandfather clock.
11. Design, build, and patent a device that will indicate the oil level in an automobile with a ten-segment bargraph. The top two LEDs will indicate overfill. The two below them are to indicate perfect oil level. The next four will indicate acceptable oil level with each one indicating, relatively, how much oil is in the pan. The last two should indicate that oil is too low and thus not allow you to start the vehicle.
12. Design and build a marketable version on the dual thermometer device that can be placed across your hot air furnace or boiler to constantly indicate the temperature difference being generated by the heat/cooling device. Both cooling and heating seasons are to be accommodated with automatic selection of the season by the device. Provide a complete set of instructions for use by a nontechnical customer.
13. Design and build the logic works for a large clockwork about 4 feet in diameter. The system is to put out a square wave TTL-level signal every 0.1 seconds. This signal will be employed by the user to feed into a clockwork driven by a stepper motor and suitable drive reduction belts and gears. The power to the stepper motors is to be provided by others. Provide a readout at the device that displays the time on an LCD display, and also provide inputs for six buttons to allow the time to be adjusted, up and down, with two buttons each for hours, minutes, and seconds. Provide an interlock switch. In the locked position, the switch will interlock the display to the 0.1-inch signal. In the unlocked position, the signal will go out (clock hands will move) but will be isolated from the LCD display. This will allow the clock to be synchronized to the display after startup, or if the power goes down, or if some other malfunction occurs, offering a way to move the clock hands on the control panel. This means that if you ask the hands to move forward 5 minutes, the controller has to put out enough pulses at a rapid rate to make this move. See the next project.
14. Design and build the amplifier needed to run the stepper motors in Project 13. Amplifier shall provide signals to the stepper motor coils and provide all the connections needed to connect to the stepper motor. Provide a way to divide the input signal frequency in case the gearing on the clockworks does not match the 0.1-second pulses from the logic works. This is to be done in the electronics within the amplifier module. Add convenience hardware and software features as you see fit to create an easy-to-use marketable amplifier module.
Finally, describe in detail five projects you think you could build using what you have learned. File your notes in your shop manual for future reference.